1. Field of the Invention
This invention relates a light emitting apparatus that includes a light emitting element and a phosphor, and particularly to a light emitting apparatus that can be applied to an LED display, a backlight device, a traffic light, a lighting switch, sensors, indicators etc.
2. Description of the Related Art
Light emitting elements used for a light emitting apparatus include inorganic LED (light emitting diode), organic LED, laser diode, inorganic thick film electroluminescence sheet, inorganic thin film electroluminescence sheet et. LED is especially advantageous in that it is long-life, compact, shock-resistant, suitable for emission of narrow spectrum band.
However, by means of the proper emission of LED, multiple light colors or multiple light colors of especially wide spectrum band cannot be realized or can be only inefficiently. This is particularly applied to the case that white light is intended to obtain.
In state of the art, a light color that is originally impossible to obtain by semiconductor LED can be obtained by wavelength conversion technique. The principles of wave length conversion technique are as follows. At least one phosphor is placed over or around LED, the phosphor absorbs the light emitted from the LED and emits light with a wavelength different from that of the absorbed light. In other words, after absorbing the light emitted from the LED, it emits photoluminescent light with another emission color.
Japanese patent application laid-open No. 2001-217466 discloses a light emitting apparatus that a light emitting element (or LED) is placed on the center axis of a reflection mirror, covered with phosphor-dispersed epoxy resin, and, in operation, the light emitted from the LED is absorbed or dispersed, so that the light with a wavelength different from that of the absorbed light, i.e., another color light is radiated in all directions.
For example, a white LED lamp known is composed such that light emitted from a blue LED is wavelength-converted by a YAG (yttrium aluminum garnet)-group phosphor. In this white LED lamp, the blue light emitted from the blue LED is wavelength-converted into yellow light and then the yellow light is mixed with the blue light to be felt white by human eyes. The phosphor is mixed into the epoxy resin or silicone resin for sealing the blue LED such that the phosphor is positioned around the blue LED.
However, in the conventional light emitting apparatus, there is a problem that the excitation light emitted from the phosphor or the light emitted from the LED is dispersed so that the light cannot be sufficiently outputted in the direction of emission observation surface.
Especially the light returning to the LED is not sufficiently reflected in the direction of emission observation surface and, therefore, the emission efficiency must be lowered.
Although the light emitting apparatus disclosed in Japanese patent application laid-open No. 2001-217466 has a reflection mirror, plenty of dispersion will be caused by the phosphor provided around the LED. Because of this, the emission efficiency must be lowered since the light is not sufficiently outputted in the direction of emission observation surface.